Bones, Joints & Movement
(See the 4 different types of joints)

Whenever the body needs to move bones, bones work with muscles, tendons and ligaments to form joints and simple machines called levers. The actual bending and straightening of the arm is an example of this simple machine. When the arm is bent the lower arm bones represent the rigid bar, the elbow joint is the fulcrum, the hand is the weight that is moved, and the force is supplied by muscles on the anterior side (front) of the upper arm.

There are six basic movements occurring in your joints. The first two, flexion and extension, are found in almost all freely moveable joints, including toes, ankles, knee, hip, truck, shoulder, elbow wrist and fingers. Flexion means the angle between the two general segments of the joint decreases, such as flexing your bicep. Extension is the opposite and the angle of the two segments thus increases such as extending your knee to stand up from a sitting position.

The second pair of movements, abduction and adduction are not as common as flexion and extension, and typically occur at the hip, shoulder and wrist. Abduction is movement away from the midline of the body, such as lifting your leg straight out to your side. Adduction is movement towards the midline of your body, such as bringing your legs closer together from a wide stance.

The last two basic movements are segment rotations. Rotations can be either medial (also known as internal), and lateral (also known as external). These type of rotations are best described around shoulder movements. If you place your palm flat on your stomach, your arm (humerus) is said to be medially rotated. If you then, while in the same position, keep your elbow close to your waist and gradually take your palm away from your stomach you are laterally rotating your arm. This medial/lateral rotation described above all takes place at the shoulder joint. See the 4 different types of joints

Here are additional terms relating to joint movements:
Flexion: when the knee bends
Extension: when the knee extends
Dorsiflexion: foot bending upwards
Plantar flexion: on your tippy toes
Hyperextension: bending your spine back
Abduction: leg moving outward from body
Adduction: leg moving inward to the body
Rotation: twisting via segment rotation
Circumduction: moving the finger in a circular motion without moving the hand
Pronation: turning the palm downward
Supination: turning the palm upward
Eversion: turning foot with sole outward
Inversion: turning foot with sole inward
Retraction: moving scapula together
Protraction: moving scapula apart
Elevation: raising a body part (i.e. raising shoulders)
Depression: lower a body part (i.e. drooping shoulders)




Reference Source 7,58,82